Hydraulic torque amplifiers



June 23,1970 J. F. JACKSON 3,516,333

HYDRAULIC TORQUE AMPLIFIERS Filed March 11. 1968 v s Sheets-Sheet 1 FIG! 2/ ,5 J 4 2 9 I 24 l0 l7 6 7 J A/ I I I Z l 5 ,1 p 7 l0 l4 2; 71 4 22 l9 l 20 :g Ge

&

June 23, 1970 J. F. JACKSON HYDRAULIC TORQUE AMPLIFIERS Filed llarch 11. 1968 3 Sheets-Sheet 2 mm &

Jung 23, 1970 J. F. JACKSON 3,516,333

HYDRAULIC TORQUE AMPLIFIERS Filed March 11, 1968 3 Sheets-Sheet 5 United States Patent 3,516,333 HYDRAULIC TORQUE AMPLIFIERS Joseph F. Jackson, Halifax, England, assignor to Pratt Precision Hydraulics Limited, Halifax, England, a British company Filed Mar. 11, 1968, Ser. No. 711,962 Claims priority, application Great Britain, Apr. 7, 1967, 15,982/ 67 Int. Cl. F1511 9/10; F0lb 3/00, 13/04 U.S. Cl. 91--380 4 Claims ABSTRACT OF THE DISCLOSURE The hydraulic torque amplifier includes a control valve having a spool which is axially movable from a neutral position by an input displacement which rotates a gear member mounted for rotation on a screw-threaded extension of the valve spool. Sideways movement of the gear member on the screw-threaded member is prevented with the result that the applied input displacement is caused to move the valve spool axially without any rotation of the valve spool and so to pass pressurised fluid to drive the motor of the hydraulic torque amplifier. The hydraulic motor itself rotates the valve spool in such a direction that the valve spool tends to be restored to the neutral position.

SUMMARY OF THE INVENTION This invention relates to hydraulic torque amplifiers. Essentially an hydraulic torque amplifier comprises an hydraulic motor and a control valve which causes pressurised fluid to be applied to the hydraulic motor in response to an applied input angular displacement so that the hydraulic motor may reproduce the input angular displacement with increased energy.

It is an object of the present invention to provide an hydraulic torque amplifier which is more efficient in operation in that it always retains a correct following error between the input torque and the output torque, and in that the energy dissipated in the amplifier during operation is kept to a practicable minimum.

In many applications of hydraulic torque amplifiers in which high speed operation is required, for example in numerical position control systems where a digital signal is converted into an analogue shaft position, it is very desirable for the energy of the input angular displacement to be kept as low as possible. By using as the control for the hydraulic motor a valve having a valve spool the axial position of which effects the control and by causing the applied input displacement to change the axial position of the valve spool without rotating the valve spool, the hydraulic torque amplifier of the present invention enables the applied input torque to be substantially reduced as compared with known hydraulic torque amplifiers.

In accordance with the present invention, therefore, there is provided an hydraulic torque amplifier comprising an hydraulic motor and an hydraulic control valve having a valve spool which is movable axially from a neutral position by an applied input displacement to apply pressurised fluid to the hydraulic motor, and which is rotatable only by the hydraulic motor to restore the valve spool to the neutral axial position in which no pressurised fluid is applied to the hydraulic motor.

More particularly the present invention comprehends an hydraulic torque amplifier comprising an hydraulic motor, an hydraulic control valve having a valve spool the axial position of which controls the application of pressurised fluid to the hydraulic motor, and means independent of rotation of the valve spool for converting an applied input displacement into a linear movement of the valve spool along its axis for causing pressurised fluid to be applied to the hydraulic motor.

The operation of an hydraulic torque amplifier according to a preferred embodiment of the present invention is that an input angular displacement is applied to a gear member which is mounted for rotation on a screwthreaded member to move the screw-threaded member linearly, the screw-threaded member is associated with a valve spool so that the valve spool is moved linearly from a neutral position by the linear movement of the screw-threaded member, the linear movement of the valve spool controls the application of pressurised fluid to an hydraulic motor which reproduces the applied input displacement, and the hydraulic motor is so connected to the valve spool that rotation of the hydraulic motor, as a result of application of the pressurised fluid, tends to restore the valve spool to the neutral position.

In the specific embodiment of the invention which will be described the hydraulic torque amplifier comprises an hydraulic motor, an hydraulic control valve having a valve spool which is movable axially from a neutral position to apply pressurised fluid to the hydraulic motor and which is rotatable by the hydraulic motor to restore the valve spool to the neutral position, a gear member which is mounted for rotation on a screw-threaded member connected to the valve spOOl and which is constrained against movement in the direction of the axis of rotation, and an input torque means for applying an input displacement to rotate the gear member and so to move the valve spool axially to apply pressurised fluid to the hydraulic motor to reproduce the applied input displacement.

In a particular application where the hydraulic torque amplifier is used as part of an electro-hydraulic pulse motor, the input torque means comprises an electrical stepping motor which may have any desired number of electrical phases, for example three, five or six.

The gear member may be constrained against movement along its axis of rotation by being located between fixed surfaces, but preferably the gear member is constrained against movement along its axis of rotation by roller thrust bearings which are included between relatively fixed abutment faces and the faces of the gear member.

Advantageously the valve spool of the control valve has peripheral grooves which are so shaped that the forces acting axially on the valve spool as a result of the movement of pressurised fluid are minimal.

In order that the present invention may be more clearly understood the following detailed description is made, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 illustrates diagrammatically an hydraulic torque amplifier in accordance with the present invention with the valve spool in the neutral position;

FIG. 2 shows the hydraulic torque amplifier of FIG. 1 with the valve spool moved to the operating position which is to the right of the neutral position shown in FIG. 1;

FIG. 3 is a view of an hydraulic torque amplifier in accordance with the present invention included in an electro-hydraulic pulse motor;

FIG. 4 is a sectional view of the apparatus of FIG. 3 taken along the line IV-IV of FIG. 3, and

FIG. 5 is a sectional view of the apparatus of FIG. 3 taken along the line VV of that figure.

In the drawings the same or similar parts are designated by like reference numerals.

Referring to the accompanying drawings, and more particularly to FIG. 1, an angular input displacement is 3 applied from an output shaft 1 of a controlling member 2, which is conveniently an electrical stepping motor, through a gear 3 mounted on the output shaft 1 to a gear member 4 which has a threaded bore in engagement with a screw-threaded member 5. The screw-threaded member 5 constitutes an extension of a valve spool 6 of a control valve. The gear member 4 is thus mounted for rotation on the screw-threaded member 5, and the gear member 4 is constrained against movement in the direction of its axis of rotation on the screw-threaded member 5 by fixed abutment faces 7.

At its other end the valve spool 6 is in sliding engagement with an extension shaft 8 of a positive displacement type hydraulic motor 9. The extension shaft 8 of the hydraulic motor 9 is in sliding engagement with a splined bore 10 in the end of the valve spool 6 opposite to that end which carries the screw-threaded member 5. Accordingly rotation of the hydraulic motor will rotate the extension shaft 8 and the output shaft 11 of the hydraulic motor and will produce a corresponding rotation of the valve spool 6.

The valve spool 6 is free both to rotate and to slide in a close fitting valve body or sleeve 12 in which annular grooves 13, 14, 15, 16 and 17 are formed. The annular groove is connected to a source of hydraulic pressure (not shown) by means of a conduit 18 which constitutes the inlet to the valve, and the annular grooves 13 and 17 are joined by a conduit 19 which, in turn, is connected to a conduit which serves as the hydraulic fluid return line or outlet from the control valve. The annular grooves 14 and 16 are connected by respective conduits 21 and 22 to the two ports of the hydraulic motor.

The valve spool 6 has annular peripheral grooves 23, '24 and by which pairs of the annular grooves 13 to 17 formed in the valve body 12 may be selectively connected when the valve spool 6 is moved axially to the right or left of its neutral position which is shown in FIG. 1. When the valve spool 6 is moved to the right of its neutral position the annular grooves 15 and 16 in the valve body 12 are connected by the annular peripheral groove 24 in the valve spool 6, and the grooves 14 and 13 in the valve body 12 are connected by the annular peripheral groove 23 in the valve spool 6. This position is shown in FIG. 2 to which detailed reference will be made below. Similarly when the valve spool 6 is moved to the left of the neutral position shown in FIG. 1 annular grooves 14 and 15 are connected by the annular peripheral groove 24, and the annular grooves 16 and 17 are connected by the annular peripheral groove 25.

Referring now to FIG. '2, the position is shown in which an angular displacement of the gear member 4 applied by the controlling member 2 via the shaft 1 and the gear 3 produces an axial displacement of the Screw-threaded member 5 and also of the valve spool 6 to a position to the right of the neutral position shown in FIG. 1. This axial displacement of the valve spool 6 selectively connects the ports of the hydraulic motor 9 to the inlet or pressure conduit 18 and the outlet or return conduit 20 by means of metering orifice openings 27 and 26.

Hydraulic fluid is thus allowed to flow from the pressure source through the conduit 18, the metering orifice 27 and conduit 22 to the hydraulic motor 9, and from the hydraulic motor 9 through conduit 21, metering orifice 26 and conduit 19 to the outlet conduit 20 which serves as the hydraulic fluid return line. The conduits 21 and 22 are connected to the hydraulic motor 9 in such a manner that the output shaft 11 and the extension shaft 8 of the hydraulic motor 9 are rotated in the direction in which the extension shaft 8 rotates the valve spool 6 and the screw-threaded member 5 to cause the valve spool 6 to move axially to the left as shown in FIGS. 1 and 2 as a result of the engagement of the screwthreaded member 5 in the threaded bore of the gear member 4. The movement of the valve spool 6 to the left will cause the metering orifices 26 and 27 to close.

Accordingly the output shaft 11 of the hydraulic motor 9 follows the motion of the gear member 4 and the device operates as a closed-loop position control system.

When the controlling member 2 rotates its output shaft 1 and the gear 3 in the opposite direction to that considered in relation to FIG. 2 the valve spool 6 moves to the left of its neutral position, and a similar action occurs which causes the output shaft 11 of the hydraulic motor 9 to be rotated in the opposite direction to that shown in FIG. 2.

Referring now to FIGS. 3 to 5 there is shown an hydraulic torque amplifier, which is essentially similar to the hydraulic torque amplifier described with reference to FIGS. 1 and 2, arranged to be operated by an electric stepping motor 30 which is the particular controlling member employed in an electro-hydraulic pulse motor. The output shaft 1 of the electric stepping motor 30 and the gear 3 rotate the gear member 4 in a manner similar to that already described. In the embodiment of FIGS. 3 to 5, however, the gear member 4 is located in a constant position axially of the valve spool 6 by roller thrust bearings 31 and 32 which are conveniently needle roller bearings. The roller bearings 31 are located against fixed faces 33, and the roller bearings 32 are located against relatively fixed faces 34 which are constantly urged to press the roller bearings 32 against the face of the gear member 4 by disc springs 35 seated on the fixed valve body.

In the preferred embodiment of the invention illustrated in FIGS. 3 to 5 the annular peripheral grooves 23 and 25 on the valve spool 6 have specially shaped surfaces 37 and 38 which are smoothly curved, as shown in FIGS. 3 and 4, in order that the movement of the pressurized fluid may exert minimum axial forces on the valve spOOl 6. The inclusion of the shaped surfaces 37 and 38 enables the applied input torque from the electric stepping motor 30 which is necessary to move the valve spool 6 axially to be kept extremely small.

As a matter of normal engineering practice, conventional anti-backlash devices may be included in the hydraulic torque amplifier. Such devices may be included, for example, between the screw-threaded member 5 and the gear member 4 and between the extension shaft 8 and the splined bore 10. Also means may be provided for controlling the distance between the centers of gear 3 and gear member 4 so that backlash between these integers is kept to a minimum during operation. Such means is also well known in the art. The inclusion of these devices enables a greater tolerance in manufacture to be accepted, so that high quality performance is obtainable without very high precision machining being necessary.

In FIGS. 3 and 4 the part of the apparatus which constitutes the hydraulic motor 9 is indicated by the line 39. The hydraulic motor confined within the line 39 has certain novel features.

However, the hydraulic torque amplifier of the present invention may incorporate any known hydraulic motor rather than the particular hydraulic motor 39 which is illustrated, and the hydraulic torque amplifier which is described is not limited to incorporation of the hydraulic motor 39 and use with the electric stepping motor 30.

The hydraulic toque amplifier of the present invention may be operated by a very small applied torque, because very much less torque is necessary to move the valve spool axially than would be necessary for example to rotate the valve spool. Also it is to be noted that, in the steady state condition in which the output shaft 1 of the controlling member and the output shaft 11 of the hydraulic motor are rotating at the same speed, no input energy is being dissipated in the arrangement of the present invention, because there is then no relative rotation between the gear member 4 and the valve spool 6 which is being driven by the hydraulic motor through the extension shaft 8.

A further advantage of the hydraulic torque amplifier as herein described is that the inertia of the elements which are driven by the controlling member 2 is less than in any of the known arrangements in which rotation of a valve element such as a valve spool is essential for causing the pressurized fluid to be applied to the hydraulic motor. The effect of this low inertia of the device of the present invention is that faster acceleration of the controlling member is permitted and this is particularly advantageous when the controlling member is an electric stepping motor.

I claim:

1. An hydraulic torque amplifier wherein an applied input angular displacement is reproduced as a similar output angular displacement generated by the application of a pressurized fluid and having increased energy as compared with the applied input angular displacement, the amplifier comprising an hydraulic motor having a rotor part including an output shaft upon which the input angular displacement is to be reproduced, an hydraulic control valve for controlling, in accordance with the applied input angular displacement, the application of pres surized fluid to the hydraulic motor and the consequent angular movement of the rotor part of the hydraulic motor, the hydraulic control valve including a valve spool which is movable axially from a neutral position to apply the pressurized fluid to the hydraulic motor, means, including a screw-threaded member which is connected to the valve spool, a gear member which is carried on the screw-threaded member for rotation relative thereto, the gear member having a threaded bore engaging the thread of the screw-threaded member, and means constraining the gear member against any movement in the direction of its axis of rotation, for changing the axial position of the valve spool without rotating the valve spool, an input torque means for applying the input angular displacement to rotate the gear member and so to move the valve spool axially to apply said pressurized fluid to the hydraulic motor and thereby to rotate the rotor part of the hydraulic motor and generate the output angular displacement, and means connecting the rotor part of the hydraulic motor to the valve spool whereby rotation of the rotor part of the hydraulic motor in the generation of the output angular displacement ensures corresponding rotation of the valve spool in a direction to provide the axial movement of the valve spool which will restore the valve spool to the neutral position within the hydraulic control valve from which the valve spool was moved as a result of the applied input angular displacement.

2. An hydraulic torque amplifier according to claim 1, wherein the input torque means comprises an electrical stepping motor.

3. An hydraulic torque amplifier according to claim 1, included between relatively fixed abutment faces and the faces of the gear member.

4. An hydraulic torque amplifier according to claim 1,

wherein the valve spool of the control valve has peripheral grooves which are so shaped that the forces acting axially on the valve spool as a result of the movement of pressurized fluid are minimal.

References Cited UNITED STATES PATENTS PAUL E. MASLOUSKY, Primary Examiner U.S. Cl. X.R. 91-175, 176

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 ,516 ,333 June 23 1970 Joseph F. Jackson It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 6, lines 14 to 16, claim 3 should read:

3 An hydraulic torque amplifier according to claim 1, wherein the means constraining the gear member against movement in the direction of its axis of rotation comprises roller thrust bearings which are included between relatively fixed abutment faces and the faces of the gear member.

Signed and sealed this 6th day of October 1970.

(SEAL) Attest:

Edward M. Fletcher, J1. JR.

Attesting Officer Commissioner of Patents 

